Why are U.S. Northwestern metropolitan areas (cities) set back from the coast? Everywhere in the U.S. major cities tend to sit close to coasts, because this is optimal for trade. Major continental cities also tend to be trade hubs for other reasons (rivers, crossroads, etc.).
Here's a map I made of Metropolitan Statistical Areas (MSA component counties are shaded and circles represent total MSA populations).
As you can see, Northwestern metropolitan counties form a strip which is separated from the coast by a breadth of at least one county, a pattern which cannot be found anywhere else in the U.S. Yet Seattle and Portland are substantial cities, comparable to other major coastal cities, if not the biggest.
Perhaps individual explanations can be found, such as that Seattle actually sits on the deep-set Puget Sound and Portland on the navigable Willamette River. Still, I am intrigued whether there is some kind of generic explanation for this pattern, e.g. no natural port on the coast or unnavigable currents or uninhabitable coast for some reason, but the coast is not steep and even seems to have plenty of estuaries. (An intermediate explanation is that population clustered along Interstate 5, but this only pushes the question back further to why the Interstate 5 was located there in the first place.)